Preparation method of polyphenylene sulfide heat-resistant diaphragm for metal-based battery

Abstract

The invention relates to a preparation method of a polyphenylene sulfide heat-resistant diaphragm for a metal-based battery. The preparation method comprises the following steps: (1) preparing a binder; (2) preparing coating slurry; (3) coating a polyphenylene sulfide porous membrane with the coating slurry, and forming a coating layer on the surface of the polyphenylene sulfide porous membrane to obtain a coating membrane; (4) immersing the coated film in a coagulating bath to carry out non-solvent induced phase transformation; and (5) drying to obtain the polyphenylene sulfide heat-resistant diaphragm. The polyphenylene sulfide heat-resistant diaphragm prepared by the invention has excellent thermal stability, electrochemical stability and high capacitance, and the thermal stability and safety of a battery can be remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of functional separator materials for metal-based batteries, and particularly relates to a preparation method of a polyphenylene sulfide heat-resistant separator for metal-based batteries. Background Art

[0002] With the vigorous development of the new energy industry, the application of batteries is indispensable for various energy storage technologies. It is worth noting that lithium batteries and low-cost sodium-ion batteries have become the focus of research and industrialization. With the large-scale application of batteries, the requirements for their performance are becoming increasingly strict. The core components of a battery include a positive electrode material, a negative electrode material, a separator, and an electrolyte. Among them, although the separator only accounts for 10% to 20% of the battery cost, its performance has a direct and important impact on key indicators such as the battery's capacitance, cycle life, and safety performance. Therefore, developing high-performance separators is crucial for improving the overall performance of batteries.

[0003] Currently, the mainstream materials for lithium, sodium, and zinc battery separators are polyolefins, specifically including polypropylene, polyethylene, and their coated modified products. Polyolefin materials have been widely used in the field of battery separators due to their excellent mechanical properties, good ionic conductivity, and stable chemical properties. However, the thermal stability of polyolefin separators is relatively low, and they are prone to thermal shrinkage in high-temperature environments, which may cause accidental contact between the positive and negative electrodes of the battery, leading to safety hazards such as short circuits and battery combustion and explosion.

[0004] In view of this, it is particularly important to develop a new type of battery separator with both high thermal stability and excellent mechanical properties. This new type of separator will be able to maintain structural stability under high-temperature conditions, effectively prevent internal short circuits in the battery, and thus greatly improve the safety and reliability of the battery. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a polyphenylene sulfide heat-resistant separator for metal-based batteries to achieve structural stability under high-temperature conditions, effectively prevent internal short circuits in the battery, and improve the safety and reliability of the battery.

[0006] The present invention provides a preparation method of a polyphenylene sulfide heat-resistant separator for metal-based batteries, comprising the following steps:

[0007] (1) Prepare a binder by adding a high molecular polymer and a pore-forming agent to a solvent;

[0008] (2) Add inorganic ceramic particles to the above binder to make a coating slurry;

[0009] (3) Coat the coating slurry on a polyphenylene sulfide porous membrane to form a coating layer on its surface, obtaining a coated membrane;

[0010] (4) Prepare a coagulation bath and immerse the coated film in the coagulation bath for non-solvent induced phase inversion;

[0011] (5) Dry the coated film to obtain a polyphenylene sulfide heat-resistant separator.

[0012] Preferably, in the binder of step (1), the proportion of the high molecular polymer is 10 wt% - 20 wt%, and the proportion of the pore-forming agent is 0 wt% - 20 wt%.

[0013] Preferably, the high molecular polymer includes one of polyvinylidene fluoride (PVDF), polysulfone (PSU), polyacrylic acid (PAA), polyvinyl alcohol (PVA), or polytetrafluoroethylene (PTFE).

[0014] Preferably, the pore-forming agent includes one of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), dimethyl carbonate (DMC), or dibutyl phthalate (DBP).

[0015] Preferably, in step (1), the solvent includes one of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), or dimethyl carbonate (DMC).

[0016] Preferably, in step (2), the content of the inorganic ceramic particles in the coating slurry is 70 wt% - 90 wt%, and the content of the binder is 10 wt% - 30 wt%.

[0017] More preferably, the inorganic ceramic particles include one of alumina, magnesia, zirconia, boron nitride, or iron oxide.

[0018] Further, in step (3), the coating method is one of spray coating process, dip coating process, roll coating process, or extrusion coating process; the coating layer is one of single-layer coating or double-layer coating.

[0019] More preferably, the thickness of the coating layer is 20 - 120 μm.

[0020] Further, in step (4), the coagulation bath is absolute ethanol, and the immersion time of the coated film in the coagulation bath is 5 - 12 h.

[0021] Further, in step (5), the drying temperature is 50 - 100 °C.

[0022] The present invention provides a polyphenylene sulfide heat-resistant separator for a metal-based battery prepared by the above preparation method.

[0023] The present invention also provides an application of the above polyphenylene sulfide heat-resistant separator in a metal-based battery.

[0024] Preferably, the metal-based battery includes, but is not limited to, lithium batteries, sodium batteries, or zinc batteries.

[0025] Polyphenylene sulfide (PPS) is a unique thermoplastic polymer with a structure formed by alternating benzene rings and sulfur atoms, exhibiting unique physical and chemical properties. Specifically, PPS has a glass transition temperature as high as 85 °C and a melting temperature of up to 285 °C, showing excellent heat resistance stability. Compared with other aromatic polymers, PPS can still maintain good chemical corrosion resistance and solvent stability at a high temperature of 200 °C and is not easily soluble in a variety of organic solvents. In addition, PPS also has excellent flame retardancy and high temperature resistance, can maintain the structural integrity in a high temperature environment, and effectively prevent thermal runaway. At the same time, it has good mechanical strength and excellent processing performance, facilitating various forming and processing treatments, providing more possibilities for the manufacture of battery separators. Given these excellent comprehensive properties of PPS, it has been widely used in many industrial fields such as electronics, electrical appliances, and automobiles. PPS is used as a battery separator material in the present invention to improve the thermal stability and safety of the battery.

[0026] Beneficial effects

[0027] (1) The present invention selects polyphenylene sulfide with extremely excellent heat resistance as the separator substrate, and the obtained separator has excellent heat resistance and does not shrink at a high temperature of 170 °C.

[0028] (2) The tensile strength of the polyphenylene sulfide heat-resistant separator prepared in the present invention has completely exceeded that of the commonly used glass fiber separator for sodium batteries, and the uniform separator pore size and tortuous pore structure are conducive to the uniform distribution of sodium ions during the charge and discharge process of the battery.

[0029] (3) The polyphenylene sulfide heat-resistant separator prepared in the present invention has significantly better electrochemical stability and high capacitance than the glass fiber separator. Description of the Drawings

[0030] Figure 1 It is a scanning electron microscope image of the polyphenylene sulfide heat-resistant separator in Example 3 of the present invention.

[0031] Figure 2 It is a thermal stability test diagram of the polyphenylene sulfide heat-resistant separator in Example 3 of the present invention.

[0032] Figure 3 It is a tensile strength test diagram of the polyphenylene sulfide heat-resistant separator in Example 3 of the present invention and the separator in Comparative Example 1.

[0033] Figure 4 It is a cyclic charge and discharge capacity data diagram of sodium batteries assembled with the polyphenylene sulfide heat-resistant separator in Example 3 of the present invention and the glass fiber separator in Comparative Example 1 respectively.

[0034] Figure 5 Time-voltage curves of sodium batteries assembled with the polyphenylene sulfide heat-resistant separator in Example 3 of the present invention and the glass fiber separator in Comparative Example 1 respectively. Detailed implementation manners

[0035] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0036] The tensile strength of the polyphenylene sulfide heat-resistant separator prepared in the examples and the separator in the comparative example was tested as follows: It was carried out in accordance with the provisions of GB / T1040.3-2006. A separator specimen with a width of 10 mm was used for the tensile strength test on an electronic tensile machine. The initial distance between the clamps was 100 mm, and the test speed was 250 mm / min.

[0037] Sodium batteries were assembled with the polyphenylene sulfide heat-resistant separator prepared in the examples and the separator in the comparative example respectively, and the steps are as follows:

[0038] (1) Preparation of the positive electrode sheet: Sodium vanadium phosphate was selected as the positive electrode material. The slurry used was prepared by dissolving sodium vanadium phosphate, conductive carbon black, and polyvinylidene fluoride binder in N-methylpyrrolidone according to a weight ratio of 8:1:1; then the positive electrode slurry was coated on aluminum foil with a 200-μm doctor blade and dried in a forced-air oven at 100 °C for 10 hours; after the solvent was completely volatilized, the positive electrode sheet was cut into positive electrode sheets with a diameter of 10 mm. The electrolyte used was a 1M sodium hexafluorophosphate solution, where the solvent was a mixed solvent of ethylene carbonate and diethyl carbonate, and their volume ratio was 1:1. The additive was 5% fluoroethylene carbonate, and the amount of electrolyte used was 100 μL.

[0039] (2) The negative electrode was a sodium sheet with a diameter of 16 mm.

[0040] (3) Preparation of the button battery: The above positive electrode sheet, negative electrode sheet, electrolyte, and separator sheet were assembled into a CR2025 button battery, that is, a sodium / sodium vanadium phosphate battery, in a glove box with a dry argon atmosphere.

[0041] Test conditions: The battery cycle test used a BlueTEC CT3002A test platform, and the charge-discharge voltage range was 2.5 - 4.5 V. Charge-discharge cycle tests were carried out under a current condition of 1C (1C = 117.6 mAh g -1 ).

[0042] (4) Preparation of symmetric battery: The positive and negative electrodes are sodium sheets with a diameter of 10 mm, and the electrolyte is the electrolyte described in step (1). Assemble the above sodium sheets, electrolyte, and separator into a sodium-sodium symmetric battery.

[0043] Test conditions: Charge and discharge cycling tests are carried out under the condition of a current density of 1 mA cm -2 of.

[0044] Example 1

[0045] In this example, the preparation method of the polyphenylene sulfide heat-resistant separator includes the following steps:

[0046] (1) Weigh a quantitative amount of polysulfone according to a concentration of 20 wt% and dissolve it in NMP. The dissolution temperature is preferably 50 °C, and stir for 5 h to mix into a binder;

[0047] (2) Weigh zirconia in proportion and add it to the above binder, and mix and stir with a slurry mixer for 10 min to prepare a coating slurry, where zirconia accounts for 70 wt% of the coating slurry;

[0048] (3) Uniformly coat the coating slurry on the surface of the polyphenylene sulfide porous membrane by a double-sided roll coating method to obtain a coated membrane;

[0049] (4) Immerse the coated membrane in an ethanol coagulation bath for non-solvent induced phase transition;

[0050] (5) Carry out hot air drying on the coated membrane in step (4), the drying temperature is 50 °C, and the drying time is 2 h to obtain the polyphenylene sulfide heat-resistant separator.

[0051] Example 2

[0052] In this example, the preparation method of the polyphenylene sulfide heat-resistant separator includes the following steps:

[0053] (1) Weigh a quantitative amount of polysulfone and polyvinylpyrrolidone (PVP) according to a mass ratio of 15:5, and then dissolve them in an NMP solution. The dissolution temperature is preferably 50 °C, and stir for 5 h to mix into a binder;

[0054] (2) Weigh zirconia in proportion and add it to the above binder, and mix and stir with a slurry mixer for 10 min to prepare a coating slurry, where zirconia accounts for 70 wt% of the coating slurry;

[0055] (3) Uniformly coat the coating slurry on the surface of the polyphenylene sulfide porous membrane by a double-sided roll coating method to obtain a coated membrane;

[0056] (4) Immerse the coated membrane in an ethanol coagulation bath for non-solvent induced phase transition; Due to the weak interaction between polyvinylpyrrolidone and polysulfone, when the polymer solution contacts the non-solvent, polyvinylpyrrolidone is more likely to separate from polysulfone to form a pore structure;

[0057] (5) Hot air dry the coating film in step (4) at a drying temperature of 50 °C and a drying time of 2 h to obtain a polyphenylene sulfide heat-resistant separator.

[0058] Example 3

[0059] In this example, the preparation method of the polyphenylene sulfide heat-resistant separator refers to Example 2, and the difference is that the mass ratio of polysulfone to polyvinylpyrrolidone in step (2) is 15:3.

[0060] Example 4

[0061] In this example, the preparation method of the polyphenylene sulfide heat-resistant separator refers to Example 3, and the difference is that zirconia accounts for 80 wt% of the coating slurry in step (3).

[0062] Comparative Example

[0063] Comparative Example 1 is a commercial glass fiber separator (GF) with a thickness of 675 μm.

[0064] Comparative Example 2 is a polyethylene separator (PE) with a thickness of 14 μm.

[0065] Comparative Example 3 is a polypropylene separator (PP) with a thickness of 25 μm.

[0066] The formulation parameters of the separator coating liquids of Examples 1-4 and Comparative Examples 1-3 are shown in Table 1:

[0067] Table 1

[0068]

[0069] The present invention successfully prepared a polyphenylene sulfide heat-resistant separator with high heat resistance by using a double-sided coating technology. Taking Example 3 as an example, the morphology of the prepared polyphenylene sulfide heat-resistant separator is as Figure 1 shown, where zirconia effectively regulates the pore structure of the polyphenylene sulfide heat-resistant separator, realizing the uniform distribution of ion flux. In addition, Figure 2 shows the excellent thermal stability of the separator. In contrast, the PE separator in Comparative Example 2 and the PP separator in Comparative Example 3 showed significant thermal shrinkage at 140 °C, and the PP separator was in a molten state at 170 °C; however, the polyphenylene sulfide heat-resistant separator could still maintain its complete form even at 170 °C. Due to the mechanical strength of the polyphenylene sulfide porous membrane, the tensile strength of its coated separator was as high as 22.5 MPa, as Figure 3 shown, and the Young's modulus reached 0.44 MPa. In contrast, the Young's modulus of the commercial glass fiber separator was only 0.08 MPa, much lower than that of the polyphenylene sulfide heat-resistant separator, and it could not effectively inhibit the uncontrolled growth of sodium dendrites. In addition, the thickness of the glass fiber separator was as high as 675 μm, which would reduce the overall energy density of the battery.

[0070] The improvement in the performance of the polyphenylene sulfide heat-resistant separator prepared by the present invention has led to a certain improvement in the electrochemical performance of the assembled battery. For example, when charging and discharging under a 1C current condition, the sodium / sodium vanadium phosphate full battery assembled with the polyphenylene sulfide heat-resistant separator prepared in Example 3 still had a capacity retention rate of 88.91% after 1000 cycles, while the battery assembled with the commercial glass fiber separator had a capacity retention rate of only 71.84% after 1000 cycles, as Figure 4 shown. In addition, the polyphenylene sulfide heat-resistant separator also inhibits the growth of dendrites. As Figure 5 shown, the symmetric battery composed of the polyphenylene sulfide heat-resistant separator was cycled for more than 700 hours at a current density of 0.25 mA cm -2 , and the polarization voltage was stable at 119 mV. The glass fiber separator started to short-circuit after 456 hours of cycling. This shows that the polyphenylene sulfide heat-resistant separator prepared by the present invention has significantly better electrochemical stability and high capacitance than the glass fiber separator.

Claims

1. A method for preparing a polyphenylene sulfide heat-resistant separator for a metal-based battery, comprising the following steps: (1) Adding a high molecular weight polymer and a pore-forming agent into a solvent to prepare a binder; (2) adding inorganic ceramic particles to the above-mentioned binder to prepare a coating slurry; (3) coating the coating slurry on the polyphenylene sulfide porous membrane to form a coating layer on the surface of the membrane to obtain a coating membrane; (4) preparing a coagulation bath, and immersing the coated film in the coagulation bath to perform a non-solvent induced phase transition; (5) The coated film is dried to obtain a polyphenylene sulfide heat-resistant separator.

2. The preparation method according to claim 1, characterized in that: In the step (1), the high molecular weight polymer accounts for 10 wt% to 20 wt% of the binder, and the pore-forming agent accounts for 0 wt% to 20 wt%.

3. The preparation method according to claim 2, characterized in that: The high molecular polymer includes one of polyvinylidene fluoride, polysulfone, polyacrylic acid, polyvinyl alcohol or polytetrafluoroethylene.

4. The preparation method according to claim 2, characterized in that: The pore-forming agent includes one of polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, dimethyl carbonate or dibutyl phthalate.

5. The preparation method according to claim 1, characterized in that: The solvent in step (1) includes one of N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide or dimethyl carbonate.

6. The preparation method according to claim 1, characterized in that: In the step (2), the content of the inorganic ceramic particles in the coating slurry is 70 wt% to 90 wt%, and the content of the binder is 10 wt% to 30 wt%.

7. The preparation method according to claim 6, characterized in that: The inorganic ceramic particles include one of aluminum oxide, magnesium oxide, zirconium oxide, boron nitride or iron oxide.

8. The preparation method according to claim 1, characterized in that: The coating method in step (3) is one of spray coating, dip coating, roller coating or extrusion coating; the coating layer is one of single-layer coating or double-layer coating.

9. A heat-resistant polyphenylene sulfide diaphragm prepared according to the preparation method according to any one of claims 1 to 8.

10. Use of the heat-resistant polyphenylene sulfide separator as claimed in claim 9 in a metal-based battery.

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